Research will be continued on the development of a general method for isolation of B cells containing specific receptors. The method, in brief, consists in coating polystyrene tubes with specifically purified antihapten antibody. A protein antigen, conjugated to hapten, is then bound to the tube. This is followed by lymphocytes bearing specific receptors for the protein antigen. The lymphocytes are recovered by the addition of hapten. The same method will be applied to the recovery of cells bearing a specific idiotypic receptor, by using antiidiotypic antibodies coupled to the hapten as the second coat on the polystyrene tube. The method will be applied to the isolation of cells bearing a desired idiotype. These will be used to repopulate irradiated mice. It is hoped that large concentrations of molecules bearing a single idiotype can be elicited in this manner. If so, these will be used in structural and genetic studies. Another investigation will be concerned with the mechanism which results in the favored production of anti-phenylarsonate antibodies (anti-Ar) in A/J mice bearing a particular idiotype. We know that A/J mice are capable of producing antibodies of many other idiotypes as well, but the same idiotype always appears in substantial concentration. One possibility to be explored is that this cross-reactive idiotype is associated with antibody of high affinity. This will be tested directly by subjecting specifically purified anti-Ar antibodies of A/J mice to isoelectric focusing. Individual fractions will be studied to determine whether the favored idiotype is of high affinity. If so, this could account for the fact that it always appears, since the corresponding lymphocytes would have a great advantage in capturing the antigen.